This application is a National Phase Application of PCT/US2011/037091, filed on May 19, 2011.
1. Field of the Disclosure
The invention relates to a test stand for the simulation of forces and moments introduced into a motor vehicle or into parts of a motor vehicle during driving operation.
2. Description of the Prior Art
Test stands of the generic type are generally used, in particular at the end of an operational integrity validation process, to reproduce as realistically as possible the forces and loads which occur in real driving operation and which act on a vehicle to be tested or on parts of a vehicle to be tested. For this purpose, real operating load simulation tests are carried out on axle or whole-vehicle test stands in order to be able to draw conclusions regarding the effects of certain loads primarily on the operational integrity and vibration behavior of the vehicle.
In general, use is made for this purpose of axle or whole-vehicle test stands (hereinafter also referred to generally as “test stands”) in which multi-axial force-time profiles at the wheel central point are realized by means of servohydraulic actuators. Here, the specifications for the force-time profiles to be realized are gathered from test track measurements during which the wheel central point forces occurring in real operation are measured by means of special measurement wheels. In a complex iterative process, corresponding generally highly dynamic activation or excitation signals for the servohydraulic actuators of the test stand are then determined such that the wheel central point forces measured on the test track are reproduced as exactly as possible on the test stand. This process, also referred to as “drive signal iteration”, can take up to one week.
For example, the document U.S. Pat. No. 5,610,330 A discloses a method for determining an excitation signal for the actuators, which engage on the wheel central point of a motor vehicle to be tested, of a road simulation test stand. Here, to determine the excitation signal, it is provided that firstly, during a driving operation measurement, a vehicle equipped with a measurement wheel is driven over a test track in order, using the data gained by means of the measurement wheel, to obtain an excitation function for the actuator of the test stand. Subsequently, a second vehicle of the same type is arranged on a test stand, and the actuators of the test stand are operated according to a start excitation signal. The response parameters generated in the vehicle arranged on the test stand are measured and compared with setpoint response parameters measured in the first vehicle while it was being driven over the test track. Depending on the deviations between the response parameters measured on the test stand and the setpoint response parameters, the excitation function for the actuators of the test stand is then varied until the measured response function is consistent with the setpoint values measured during the driving operation measurement.
Such a conventional approach which is known from the prior art has the disadvantage that, to transfer the excitation signals gained iteratively for one vehicle type to the excitation signals for a vehicle of a different type, it is generally necessary for load input data of both axles of the second vehicle type to be gained anew during a driving operation measurement. In particular, it is generally not possible—proceeding from the excitation function for a first vehicle type—to reliably calculate or transfer the excitation function for a second vehicle type.
In particular, the activation or excitation signals for the actuator or the actuators of the test stand are dependent not only on the vehicle type but rather also on the vehicle variant. That is to say, if it is sought to derive a station wagon or a minivan from a sedan, it has hitherto been necessary for the entire process for determining the excitation function, including the test track measurement, to be repeated. Since the number of different variants and also the pressure for shortening development times are increasing ever further, vehicle manufacturers are demanding test stand concepts in which the activation signals are substantially invariant with respect to design changes in the vehicle. Such approaches which are invariant with respect to the vehicle type or vehicle variant are presently unknown.
A further disadvantage of the known operational integrity check for motor vehicles is that, in the conventional approaches, in general only operational load simulation tests are possible, that is to say the load input data gained during driving operation measurements for a test subject must generally be reproduced. This disadvantageously assumes that fully roadworthy vehicles are already present. With known test stand concepts, therefore, testing on the test stand can only take place relatively late in the development process. This has the disadvantage that changes in said late phase of vehicle development can be made only with greater difficulty and consequently at high cost.
Furthermore, test stand concepts are known in which the introduction of the forces into the vehicle body takes place not by means of actuators engaging on the wheel central point but rather by means of individual wheel contact plates (cf. EP 0 892 263 A2). In the case of a test stand of said type, a test vehicle is positioned, fully equipped with tires, on the respective wheel contact plates, the wheel contact plates being provided in each case with an actuator which introduces the simulation forces and which acts in the vertical direction. A disadvantage of a first type of such known test stand concepts with wheel contact plates is that these permit only a one-dimensional excitation, that is to say a one-dimensional compression of the vehicle tires with respect to the respective spring system of the wheel suspension. In this way, the field of use is effectively restricted to the transmission of the excitation via the wheel contact plates from one specific spring system to further specific spring systems. In other words, with such known test stand concepts with wheel contact plates of the first type, it is thus not possible to introduce further excitation signals, which go beyond the one-dimensional compression, into the vehicle body in order thereby to be able to simulate as precisely as possible the effects of certain loads primarily on the operational integrity and the vibration behavior of the vehicle.
In a second type of known test stand concepts with wheel contact plates, there are provided for each wheel contact plate a plurality of additional actuators, which are connected to a common fastening structure, in order to be able, via the wheels positioned on the wheel contact plates, to introduce into the vehicle body even forces which do not act in the vertical direction (in the spring direction) (cf. DE 102 12 255 A1). For this purpose, the common fastening structure has a horizontal base plate for the fastening of the vertical actuator, and a plurality of supports which run perpendicular thereto, the additional actuators being fastened to said supports. A disadvantage of said second type of known test stand concepts with wheel contact plates is that a large structural volume is required on account of the multiplicity of required individually suspended actuators per wheel contact plate. Furthermore, the additional actuators fastened to the supports yield the further disadvantage that the forces introduced by said additional actuators cannot be correlated with vehicle-physical variables, and in particular cannot be attributed in a simple way to the simulated track profile.